Download - Understanding operating systems 5th ed ch09
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Understanding Operating SystemsFifth Edition
Chapter 9Network Organization Concepts
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Understanding Operating Systems, Fifth Edition 2
Learning Objectives
• Several different network topologies - including the star, ring, bus, tree, and hybrid - and how they connect numerous hosts to the network
• Several types of networks: LAN, MAN, WAN, and wireless LAN
• The difference between circuit switching and packet switching, and examples of everyday use that favor each
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Understanding Operating Systems, Fifth Edition 3
Learning Objectives (continued)
• Conflict resolution procedures that allow a network to share common transmission hardware and software effectively
• The two transport protocol models (OSI and TCP/IP) and how the layers of each one compare
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Understanding Operating Systems, Fifth Edition 4
Basic Terminology
• Network– Collection of loosely coupled processors– Interconnected by communication links
• Using cables, wireless technology, both
• Common goal– Provide convenient resource sharing– Control access
• General network configurations– Network operating system (NOS)– Distributed operating system (D/OS)
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Understanding Operating Systems, Fifth Edition 5
Basic Terminology (continued)
• Network operating system (NOS)– Networking capability
• Added to single-user operating system
– Users aware of specific computers and resources in network
– Access resources• Log on to remote host
• Data transfer from remote host
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Understanding Operating Systems, Fifth Edition 6
Basic Terminology (continued)
• Distributed operating system (D/OS)– Users not aware of specific computers and resources
in network• Access remote resources as if local
– Good control: distributed computing systems• Allows unified resource access
– Total view across multiple computer systems • No local dependencies for controlling and managing
resources
– Cooperative management
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Understanding Operating Systems, Fifth Edition 7
Basic Terminology (continued)
• Distributed operating system (D/OS) (continued)– Comprised of four managers with a wider scope
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Understanding Operating Systems, Fifth Edition 8
Basic Terminology (continued)
• Distributed operating system (D/OS) (continued)– Advantages over traditional systems
• Easy and reliable resource sharing
• Faster computation
• Adequate load balancing
• Good reliability
• Dependable communications among network users
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Understanding Operating Systems, Fifth Edition 9
Basic Terminology (continued)
• Remote– Other processors and resources
• Local– Processor’s own resources
• Site– Specific location in network
• One or more computers
• Host– Specific computer system at site
• Services and resources used from remote locations
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Understanding Operating Systems, Fifth Edition 10
Basic Terminology (continued)
• Node– Name assigned to computer system
• Provides identification
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Understanding Operating Systems, Fifth Edition 11
Network Topologies
• Physically or logically connected sites
• Star, ring, bus, tree, hybrid
• Topology tradeoffs – Need for fast communication among all sites– Tolerance of failure at a site or communication link– Cost of long communication lines– Difficulty connecting one site to large number of other
sites
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Understanding Operating Systems, Fifth Edition 12
Network Topologies (continued)
• Four basic criteria– Basic cost
• Expense required to link various sites in system
– Communications cost• Time required to send message from one site to
another
– Reliability• Assurance of site communication if link or site fails
– User environment• Critical parameters for successful business investment
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Understanding Operating Systems, Fifth Edition 13
Star
• Transmitted data from sender to receiver– Passes through central controller
• Hub or centralized topology
• Advantages– Permits easy routing– Easy access control to network
• Disadvantages– Requires extremely reliable central site– Requires ability to handle all network traffic
• No matter how heavy
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Understanding Operating Systems, Fifth Edition 14
Star (continued)
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Understanding Operating Systems, Fifth Edition 15
Ring
• Sites connected in closed loop• May connect to other networks
– Using bridge (same protocols)– Using gateway (different protocols)
• Data transmitted in packets– Source and destination address fields
• Packet passed from node to node– One direction only
• Every node must be functional– Bypass failed node needed for proper operation
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Understanding Operating Systems, Fifth Edition 16
Ring (continued)
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Understanding Operating Systems, Fifth Edition 17
Ring (continued)
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Understanding Operating Systems, Fifth Edition 18
Ring (continued)
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Understanding Operating Systems, Fifth Edition 19
Bus
• Sites connect to single communication line
• Messages circulate in both directions
• One site sends messages at a time successfully
• Need control mechanism– Prevent collision
• Data passes directly from one device to another– Data may be routed to end point controller at end of
the line
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Understanding Operating Systems, Fifth Edition 20
Bus (continued)
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Understanding Operating Systems, Fifth Edition 21
Tree
• Collection of buses connected by branching cable– No closed loops
• Designers create networks using bridges
• Message from any site– Received by all other sites until reaching end point
• Reaches end point controller without acceptance– Host absorbs message
• Advantage– Message traffic still flows even if single node fails
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Understanding Operating Systems, Fifth Edition 22
Tree (continued)
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Understanding Operating Systems, Fifth Edition 23
Hybrid
• Strong points of each topology in combination– Effectively meet system communications
requirements
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Understanding Operating Systems, Fifth Edition 24
Hybrid (continued)
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Understanding Operating Systems, Fifth Edition 25
Network Types
• Grouping– According to physical distances covered
• Characteristics blurring
• Network types– Local area networks (LAN)– Metropolitan area networks (MAN)– Wide area networks (WAN)
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Understanding Operating Systems, Fifth Edition 26
Local Area Network
• Single office building, campus, similarly enclosed environment– Single organization owns/operates
• Communicate through common communication line
• Communications not limited to local area only– Component of larger communication network– Easy access to outside
• Through bridge or gateway
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Understanding Operating Systems, Fifth Edition 27
Local Area Network (continued)
• Bridge– Connects two or more geographically distant LANs– Same protocols
• Bridge connecting two LANs using Ethernet
• Gateway– Connects two or more LANs or systems– Different protocols
• Translates one network protocol into another• Resolves hardware and software incompatibilities• SNA gateway connecting microcomputer network to
mainframe host
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Understanding Operating Systems, Fifth Edition 28
Local Area Network (continued)
• Data rates: 100 Mbps to more than 40 Gbps
• Close physical proximity– Very high-speed transmission
• Star, ring, bus, tree, and hybrid– Normally used
• Transmission medium: varies
• Factors determining transmission medium– Cost, data rate, reliability, number of devices
supported, distance between units
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Understanding Operating Systems, Fifth Edition 29
Metropolitan Area Network
• Configuration spanning area larger than LAN– Several blocks of buildings to entire city
• Not exceeding 100 km circumference
• Owned and operated by a single organization– Used by many individuals and organizations– May be owned and operated as public utilities
• Means for internetworking several LANs
• High-speed network often configured as a logical ring
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Understanding Operating Systems, Fifth Edition 30
Wide Area Network
• Interconnects communication facilities in different parts of a country or world– Operated as part of public utility
• Uses common carriers’ communications lines– Telephone companies
• Uses broad range of communication media– Satellite, microwaves
• WANs generally slower than LANs– Examples: ARPAnet (first WAN), Internet (most
widely recognized WAN)
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Understanding Operating Systems, Fifth Edition 31
Wireless Local Area Network
• LAN using wireless technology to connect computers or workstations – Located within range of network
• Security vulnerabilities– Open architecture; difficulty keeping intruders out
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Understanding Operating Systems, Fifth Edition 32
Wireless Local Area Network (continued)
• WiMAX standard 802.16– High bandwidth, long distances
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Understanding Operating Systems, Fifth Edition 33
Software Design Issues
• How do sites use addresses to locate other sites?
• How are messages routed and how are they sent?
• How do processes communicate with each other?
• How are conflicting demands for resources resolved?
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Understanding Operating Systems, Fifth Edition 34
Addressing Conventions
• Addressing protocols – Fulfill need to uniquely identify users– Closely related to site network topology and
geographic location
• Distinction between local and global name – Local name within its own system– Global name outside its own system
• Must follow standard name conventions (length, formats)
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Understanding Operating Systems, Fifth Edition 35
Addressing Conventions (continued)
• Example: Internet address– [email protected]– Uses Domain Name Service (DNS) protocol
• General-purpose data query service• Hierarchical
• Domain names read left to right– Logical user to host machine– Host machine to net machine– Net machine to cluster– Cluster to network
• Periods separate components
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Understanding Operating Systems, Fifth Edition 36
Routing Strategies
• Router– Internetworking device (primarily software driven)– Directs traffic
• Between two different types of LANs
• Between two network segments (different protocol addresses)
– Network layer operation– Role changes (network designs changes)
• Connects sites– To other sites and Internet
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Understanding Operating Systems, Fifth Edition 37
Routing Strategies (continued)
• Router functions– Securing information
• Generated in predefined areas– Choosing fastest route
• From one point to another– Providing redundant network connections
• Routing protocol considerations– Addressing, address resolution, message format,
error reporting• Address resolution
– Maps hardware address
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Understanding Operating Systems, Fifth Edition 38
Routing Strategies (continued)
• Message formats– Allow performance of protocol functions
• Finding new network nodes
• Determine whether they work (testing)
• Reporting error conditions
• Exchanging routing information
• Establishing connections (transmit data)
• Most widely used Internet routing protocols– Routing information protocol (RIP)– Open shortest path first (OSPF)
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Understanding Operating Systems, Fifth Edition 39
Routing Strategies (continued)
• Routing information protocol (RIP)– Path selection based on node and hop number
• Between source and destination
– Path with smallest number of hops chosen (always)– Advantage
• Easy to implement
– Disadvantages• No consideration: bandwidth, data priority, network type
• Update and reissue routing table: changes or not
• Tables propagate (router to router)
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Understanding Operating Systems, Fifth Edition 40
Routing Strategies (continued)
• Open shortest path first (OSPF)– Network state determined first– Transmission path selected– Update messages sent when changes in routing
environment occur• Reduces number of messages in internetwork• Reduces message size: not sending entire table
– Disadvantages• Increased memory usage• Bandwidth savings offset by higher CPU usage• Shortest path calculation
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Understanding Operating Systems, Fifth Edition 41
Connection Models
• Communication network concern– Moving data from one point to another– Minimizing transmission costs– Providing full connectivity
• Circuit switching– Dedicated communication path
• Established between two hosts before transmission begins
– Example: telephone system– Disadvantage
• Delay before signal transfer begins
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Understanding Operating Systems, Fifth Edition 42
Connection Models (continued)
• Packet switching• Store-and-forward technique
– Before sending message • Divide into multiple equal-sized units (packets)
– At destination• Packets reassembled into original long format• Header contains pertinent packet information
• Advantages– More flexible, reliable – Greater line efficiency– Users allocate message priority
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Understanding Operating Systems, Fifth Edition 43
Connection Models (continued)
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Understanding Operating Systems, Fifth Edition 44
Connection Models (continued)
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Understanding Operating Systems, Fifth Edition 45
Connection Models (continued)
• Datagrams– Packet destination and sequence number added to
information• Uniquely identifying message to owning packet
– Each packet handled independently– Route selected as each packet accepted – At destination
• All packets of same message reassembled
– Advantages• Diminishes congestion and provides reliability
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Understanding Operating Systems, Fifth Edition 46
Connection Models (continued)
• Datagrams (continued)– Message not delivered until all packets accounted for– Receiving node requests retransmission
• Lost or damaged packets
– Advantages• Diminishes congestion
• Sends incoming packets through less heavily used paths
• More reliability
• Alternate paths set up upon node failure
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Understanding Operating Systems, Fifth Edition 47
Connection Models (continued)
• Virtual circuit– Complete path sender to receiver
• Established before transmission starts– All message packets use same route– Several virtual circuits to any other node– Advantages
• Routing decision made once• Speeds up transmission
– Disadvantages • All virtual circuits fail upon one failure• Difficult to resolve congestion (in heavy traffic)
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Understanding Operating Systems, Fifth Edition 48
Conflict Resolution
• Device sharing requires access control methods– Facilitates equal and fair network access
• Access control techniques– Round robin– Reservation – Contention
• Medium access control protocols– Carrier sense multiple access (CSMA)– Token passing– Distributed-queue, dual bus
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Understanding Operating Systems, Fifth Edition 49
Conflict Resolution (continued)
• Round robin– Node given certain time to complete transmission– Efficient
• If many nodes transmitting over long time periods
– Substantial overhead• If few nodes transmit over long time periods
• Reservation– Good if lengthy and continuous traffic– Access time on medium divided into slots– Node reserves future time slots
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Understanding Operating Systems, Fifth Edition 50
Conflict Resolution (continued)
• Reservation (continued)– Good configuration
• Several terminals connected to host through single I/O port
• Contention– No attempt to determine transmission turn– Nodes compete for medium access – Advantages and disadvantages
• Easy implementation; works well under light to moderate traffic; better for short and intermittent traffic
• Performance breaks down under heavy loads
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Understanding Operating Systems, Fifth Edition 51
Conflict Resolution (continued)
• Carrier sense multiple access (CSMA)– Contention-based protocol – Easy implementation (Ethernet)– Carrier sense
• Node listens to/tests communication medium before transmitting messages
• Prevents collision with node currently transmitting
– Multiple access• Several nodes connected to same communication line
as peers
• Same level and equal privileges
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Understanding Operating Systems, Fifth Edition 52
Conflict Resolution (continued)
• CSMA Disadvantages– Collision
• Two or more nodes transmit at same instant
– Probability of collision increases • As nodes get further apart
– Large or complex networks• Less appealing access protocol
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Understanding Operating Systems, Fifth Edition 53
Conflict Resolution (continued)
• CSMA/CD– Modification of CSMA– Includes collision detection (Ethernet)– Reduces wasted transmission capacity– Prevents multiple nodes from colliding
• Collisions not completely eliminated (reduced)– Implemented in Apple’s cabling system: LocalTalk– Collision occurrence involves small packet
• Not actual data (in case of Apple CSMA/CA)
• No guarantee data will reach destination– Ensures error free data delivery
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Understanding Operating Systems, Fifth Edition 54
Conflict Resolution (continued)
• Token Passing– Special electronic message (token)
• Generated and passed node to node
– Only node with token allowed to transmit• Then passes token
– Fast access– Collisions nonexistent– Typical topologies
• Bus
• Ring
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Understanding Operating Systems, Fifth Edition 55
Conflict Resolution (continued)
• Token-bus– Token passed to node in turn
• Data attached; sent to destination
– Receiving node• Copies data; adds acknowledgment; returns packet to
sending node
– Sending node passes token to next node in sequence– Initial node order determination
• Cooperative decentralized algorithm
• Then determined by priority based on node activity
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Understanding Operating Systems, Fifth Edition 56
Conflict Resolution (continued)
• Token-bus (continued)– Higher overhead at each node (than CSMA/CD)– Nodes have long waits before receiving token
• Token-ring– Token moves between nodes in turn
• One direction only
– To send message• Node must wait for free token
– Receiving node copies packet message• Sets copied bit indicating successful receipt
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Understanding Operating Systems, Fifth Edition 57
Conflict Resolution (continued)
• Distributed-queue, dual bus (DQDB)
• Dual-bus configuration– Each bus transports data one direction only– Steady stream of fixed-size slots
• Slots generated at end of each bus– Marked as free and sent downstream
• Marked busy and written to
• Written by nodes ready to transmit
– Nodes read and copy data from slots– Continue travel toward end of bus: dissipate
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Understanding Operating Systems, Fifth Edition 58
Conflict Resolution (continued)
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Conflict Resolution (continued)
• DQDB advantages– Negligible delays under light loads– Predictable queuing under heavy loads– Suitable for MANs managing large file transfers – Satisfy interactive users’ needs
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Transport Protocol Standards
• Network usage grew quickly (1980s)
• Need to integrate dissimilar network devices– Different vendors
• Creation of single universally adopted architecture– OSI reference model– TCP/IP
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Understanding Operating Systems, Fifth Edition 61
OSI Reference Model
• Basis for connecting open systems– Distributed applications processing
• “Open” – Connect any two systems conforming to reference
model and related standards• Vendor independent
• Similar functions collected together– Seven logical clusters (layers)
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Understanding Operating Systems, Fifth Edition 63
OSI Reference Model (continued)
• Layer 1: The Physical Layer– Describes mechanical, electrical, functional
specifications– Transmits bits over communication line
• Examples: 100Base-T, RS449, CCITT V.35
• Layer 2: The Data Link Layer– Establishes and controls physical communications
path before data sent– Transmission error checking– Problem resolution (on other side)
• Examples: HDLC and SDLC
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OSI Reference Model (continued)
• Layer 3: The Network Layer– Addressing and routing services moving data through
network to destination• Layer 4: The Transport Layer
– Maintains reliable data transmission between end users
• Example: Transmission Control Protocol (TCP)
• Layer 5: The Session Layer– Provides user-oriented connection service– Transfers data over communication lines
• Example: TCP/IP
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OSI Reference Model (continued)
• Layer 6: The Presentation Layer– Data manipulation functions common to many
applications• Formatting, compression, encryption
• Layer 7: The Application Layer– Application programs, terminals, computers
• Access network
– Provides user interface– Formats user data before passing to lower layers
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TCP/IP Model
• Transmission Control Protocol/Internet Protocol (TCP/IP)– Oldest transport protocol standard– Internet communications basis– File-transfer protocol: send large files error free– TCP/IP
• Emphasizes internetworking• Provides connectionless services
– Organizes communication system– Three components: processes, hosts, networks– Four layers
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Understanding Operating Systems, Fifth Edition 67
TCP/IP Model (continued)
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TCP/IP Model (continued)
• Network Access Layer– Protocols provide access to communication network– Flow control, error control between hosts, security,
and priority implementation performed
• Internet Layer– Equivalent to OSI model network layer performing
routing functions– Implemented within gateways and hosts– Example: Internet Protocol (IP)
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TCP/IP Model (continued)
• Host-Host Layer– Transfer data between two processes
• Different host computers
– Error checking, flow control, manipulate connection control signals
– Example: Transmission Control Protocol (TCP)
• Process/Application Layer– Protocols for computer-to-computer resource sharing
and terminal-to-computer remote access– Examples: FTP, SMTP, Telnet
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Summary
• Network operating systems: coordinate functions – Memory Manager, Processor Manager, Device
Manager, File Manager– Must meet owner reliability requirements
• Detect node failures; change routing instructions to bypass; retransmit lost messages successfully
• Basic network organization concepts– Terminology– Network topologies and types– Software design issues– Transport protocol standards